Such devices are generally known and consist of a permanently installed fluid treatment machine, a cassette with fluid carrying channels which are sealed with a foil, and an elastic matt placed between these two items. Medical fluids to be treated can be blood, for example, but also dialysis fluids for the peritoneal as well as the haemodialysis. The relevant cassettes are advantageously formed as disposable units. Such a fluid treatment machine can also be a device for measuring of parameters of medical fluids, for example, as described in the DE 198 37 667 A1.
In these devices, a low pressure is created between the elastic matt and the cassette in order to prevent a deformation of the foil during low pressure in the channel, which leads to a channel restriction in the cassette, in order to be able to lift the foil at the adding points for the medical fluid and thus keep the access free, in order to prevent an air compliance in the pumping device and in order to be able to guarantee at special sensor positions an air-free attachment between the sensor surface and the foil.
The extraction of air requires openings on the machine and an extraction unit connected to them, a vacuum pump for example, whereby the distribution of the vacuum should be guaranteed to be as evenly as possible and positive across the entire foil surface of the cassette.